Effect of Ce Addition on Inclusions and Grain Structure in Gear Steel 20CrNiMo

Abstract

Through laboratory experiments and thermodynamic calculation, the chemical composition and morphology of inclusion and grain size in the cast melt are comprehensively characterized herein. The results show the evolution of Al 2 O 3 inclusion formed by Al deoxidation in the gear steel 20CrNiMo follows the route of Al 2 O 3 → CeAlO 3 → Ce 2 O 2 S → Ce 2 O 2 S + CeS, and thus the nucleation core of complex Ce m nS sulfides changes from CeAlO inclusion to CeOS inclusion with the increase in Ce addition. Moreover, grain size of gear steel 20CrNiMo treated by Ce addition decreases from 491.4 to 164.0 μm, because both the Ce 2 O 2 S and CeS form with Ce addition and have potential to be effective heterogeneous nucleation agents for the primary δ‐ferrite during the solidification process of gear steel 20CrNiMo. And statistical results show that the percentage of small inclusion with a diameter less than 3 μm are, respectively, 64.4%, 86.5%, 96.4%, 93.6%, and 75.6% in the steel samples with Ce content of 0, 13, 31, 77, and 203 ppm. Thus, the recommended Ce content to achieve fine inclusions and solidification structure of gear steel 20CrNiMo is 31 ppm.

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